It is known that the amylose fraction of starch retrogrades to form a starch resistant to alpha-amylase digestion, and that this resistant starch is beneficial as a dietary component contributing to the total dietary fiber content in food products. See, for example, C. S. Berry, "Putting a figure on dietary fibre," Nutrition and Food Science 93 (1985) 8-10; C. S. Berry, "Resistant Starch: Formation and Measurement of Starch that Survives Exhaustive Digestion with Amylolytic Enzymes during the Determination of Dietary Fibre," Journal of Cereal Science 4 (1986) 301-314; and N-G. Asp, et al., "Formation of Enzyme Resistant Starch During Autoclaving of Wheat Starch: Studies in vitro and in vivo," Journal of Cereal Science 6 (1987) 159-172.
U.S. Pat. Nos. 3,729,380 and 3,324,760 disclose a method for preparing a low molecular amylose by gelatinizing starch, cooling it, and selectively hydrolyzing the branched parts in amylopectin with alpha-1,6-glucosidase. U.S. Pat. 5,051,271, and PCT application WO 90/15147 of Pomeranz et al. call for a cycle, or repeated cycles, of heating and cooling to form an alpha-amylase resistant starch that can be further purified by enzyme or chemical hydrolysis.
The starch material obtained by these methods is reported by Sievert and Pomeranz, Cereal Chemistry 67 (1990) 21, to exhibit a melting transition over two zones: one at 80.degree.-107.degree. C. with a 95.degree. C.; the other at 120.degree.-166.degree. C. with a peak at 153.degree. C. The peak at 95.degree. C. disappear sample was defatted indicating this peak corresponded to the lipid complexation of amylose. The peak at 153.degree. C. corresponded to a melting endotherm exhibited by the amylase resistant fraction (i.e. retrograded amylose). These data are consistent with those shown by Ring, et al. in Carbohydrate Research 162, (1989) 277, describing the melting of an amylopectin gel at 59.degree. C. and of an amylose gel at 153.degree. C.